Nearly fat fronts

I'm pretty keen to try a nearly phat front on my Haro Mary 29er. It's mainly used for taking the dog round the forestry but I do quite like the odd rocky trail on it and would like something with a little more give than the Nevegals I am running at the moment (on Halo rims that are fairly narrow). The fork has about a centimetre of clearance on either side so it got me thinking what rim/tyre combo ca I get away with, my budget would be about £150 for a wheel and tyre tops, what are my options and actual measured widths?